The present invention relates to a stabilized fibroblast growth factor (hereinafter briefly referred to as FGF) protein composition, a method for preparing a stabilized FGF protein composition, and a method for stabilizing an FGF protein.
FGF was first isolated as a factor exhibiting strong growth promoting action on fibroblasts such as BALB/c3T3 cells [D. Gospodarowicz, Nature 249, 123 (1974)]. It is now known that the FGF exhibits growth promoting action on almost all cells derived from mesoblast. FGF is classified into basic FGF (hereinafter briefly referred to as bFGF) and acidic FGF (hereinafter briefly referred to as aFGF), based on the isoelectric point thereof. bFGF and aFGF both have strong growth promoting action and plasminogen activator inducing action on vascular endothelial cells. Together, these actions suggest a potential for the application thereof as a drug for promoting angiogenesis, as a therapeutic drug for traumas, and as a preventive and therapeutic drug for thrombosis, arteriosclerosis, etc.
Previously, the FGFs were purified to homogeneity from organs derived from animals, such as bovine pituitary. However, supply of these FGFs was limited, and there was a fear of antigenicity due to their heterozoic origin. Recently, there has been developed a method for producing FGF in large quantities. The method involves using recombinant DNA techniques to express a cloned human FGF gene in microorganisms or in animal cells. [FEBS Letters 213, 189-194 (1987); European Patent Publication (hereinafter also referred to as EP Publication) No. 237,966)].
Another way of producing FGF in large quantity is stabilizing polypeptide producing factors using an aqueous medical composition comprising a water-soluble polysaccharides in amount sufficient for stabilizing a growth factor. This composition is disclosed as being effective against the declining of activities of mitogen of the polypeptide growing factor and the declining of bioactivities [Japanese Unexamined Patent Publication No. 63-152324/1988 corresponding to EP Publication No. 267,015].
Since most of the FGF proteins are very unstable, not only they are rapidly inactivated in aqueous solution, but also their bioactivity easily is decreased by lyophilization. Further, when the FGF proteins are administered for many hours as an intravenous drip, a reduction in titer during that time is unavoidable, which causes a major problem.
The above-described aqueous medical composition comprising water-soluble polysaccharides, especially in the case of cellulose derivatives of a degree of ether substitution of at least 0.35 ether groups per anhydroglucose unit in the cellolose chain, it is difficult to form a solid medical composition in powder when the base is an FGF protein. The titer of the composition is also lowered during mixing and drying process.